Porous exfoliated poly(ε‐caprolactone)/clay nanocomposites: Preparation, structure, and properties

Abstract

Porous biodegradable poly(e-caprolactone) (PCL)/clay nanocomposites were prepared by incorporating a blowing agent into the galleries of an organoclay, followed by mixing the pretreated organoclay and PCL to give partially intercalated and exfoliated nanocomposites and subsequently degrading the blowing agent in situ to increase the exfoliation degree in the porous nanocomposites. The blowing agent played dual roles in the foaming process: formation of bubbles and facilitation of clay exfoliation, which were confirmed by X-ray diffraction and transmission electron microscopy. Such porous nanocomposites possessed significantly more uniform porous structures and smaller pore sizes compared to their polymer counterparts, which were charac-terized by X-ray micro computed tomography. They also exhibited increases of the thermal degradation temperature by 41 C, the compressive modulus by 152%, and the compressive stress at 10% strain by 177%. The relative modulusrelative density relationship of the porous nanocomposites was found to follow the Mills-Zhu model for closed cells. Such porous biocompatible and biodegradable nanocomposites will find potential applications in, for example, carriers of chemicals, drugs, and medical and diagnostic devices.

Enhancements of clay exfoliation in polymer nanocomposites using a chemical blowing agent

“…The shifts of the silanol absorption band imply that the BAs could have intercalated successfully into the galleries of the clay. These results are similar to those for another OC, Cloisite® 30B, which was pre‐treated with the same BAs before being incorporated in a poly( ϵ ‐caprolactone) (PCL) matrix to produce PCL porous solids in our previous work . It was found that the degradation of the BAs enhanced the degree of exfoliation of the OC in PCL confirming the presence of the BA in clay galleries.…”

“…, it can be observed that the untreated OC (curve (A)) exhibits a broad diffraction peak at a 2 θ value of 3.3°, corresponding to a basal spacing, d (001) , of 2.7 nm. The BA‐OCs (curves (B) and (C)) each present a (001) peak that shifts towards higher 2 θ values probably due to the removal of some surfactant molecules or impurities from the galleries . Since compared to the surfactant the molecular sizes of the BAs are smaller, the intercalation of the latter into clay galleries may not result in an increase in the basal spacing .…”

“…The commercial OC was pre‐treated with two common chemical BAs, namely SB and ADC/zinc oxide to give the SB‐ and ADC‐treated clays, following a procedure described in our previous work for another OC . Briefly, a 2.5 wt% clay THF–water suspension (THF:H 2 O = 1:1) was mixed at room temperature for 48 h with a 10 wt% SB aqueous solution or a 5 wt% ADC and zinc oxide (ADC:ZnO = 1:1) aqueous solution.…”

“…The extruded materials, together with the neat polymers, were then heated in a convection oven at 210 °C for 10 min to allow for complete degradation of the BA and facilitate the subsequent moulding process. These processing temperatures were selected and used because they were found to be optimal for the degradation of the BAs …”

Recent Developments of Foamed Polymer/Layered Silicates Nanocomposites

“…The compressive modulus and stress of the porous polymer increased, eliminating the effect of the density changes. These biocompatible porous materials are expected to find applications as biodegradable packagings and carriers of drugs, as well as medical and diagnostic devices [90].…”